The short answer is that your video mode must support that 1600x1000 (wide) or other wide numbered display and the DVD software will have to use it. Some don't.
Bob
I just hooked up a widescreen monitor to my Dell Dimension 4300 with XP Pro. Is there a way to have the desktop display in 16:9? As it is right now there are black bars on the sides or the image is stretched by the monitor to fill the screen. This is not a big deal for everyday computing (although I'd like to utilize the full potential of the monitor), but for watching DVDs the picture is either stretched or small in the middle of the screen instead of the anamorphic widescreen when played on a standalone TV/DVD player. I've been through the screen resolution options in Control Panel and haven't found a soltution. Any help is much appreciated.
Thanks in advance!

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic